This relates to the maintenance and testing of communication lines and, in particular, to the maintenance and testing of conventional telephone lines.
Communication lines require periodic testing, maintenance and repair. At first, telephone system operators employed an entirely manual process of accessing, testing and servicing subscriber lines. However, these manual procedures allowed inoperative lines to go undetected for long periods and frequently resulted in a substantial delay between the initial report of trouble on a line and the verification and identification of that trouble. Line trouble was often discovered only when a subscriber's service had been interrupted, and even after it was reported, a rapid, accurate and intelligent response to the trouble report or to a subsequent inquiry was impossible in the majority of circumstances. In addition, the speed and accuracy of certain line tests depended on the experience of the tester and upon how quickly information about the subscriber's telephone equipment could be manually retrieved from a file; and the whole process was very much labor intensive.
In an effort to acquire better line testing, maintenance and repair capabilities, in the 1970's American Telephone and Telegraph, Inc. developed and implemented Automatic Repair Service Bureaus (ARSBs) in the predecessors of the Regional Bell Operating Companies (RBOCs). See P. S. Boggs and M. W. Bowker, "Automated Repair Service Bureau: Evolution", Bell System Technical Journal, Volume 61, No. 6, Part 2, pp. 1097-1114 (July-August, 1982). The ARSBs utilized a Loop Maintenance Operating System (LMOS) and a Mechanized Loop Testing (MLT) system.
LMOS provides four basic services to the ARSBs. First, the system generates and maintains a data base containing very detailed information. Records in this data base, known as "line records," reflect such information as the telephone equipment in use at a subscriber's site, the electrical characteristics of this equipment, whether there are any unresolved reports of trouble on the line, and whether the subscriber's account shows an unpaid balance.
Second, LMOS performs computerized trouble report processing. When a trouble on a line is reported by a subscriber, an entry is made in the applicable line record. The telephone company employee receiving the subscriber's call can use the MLT system, described below, to perform some preliminary tests on the line and verify or discount the report. If the tests disclose no line trouble, the employee will inform the subscriber that the line is in working order and make an entry in the line record reflecting that fact. Alternatively, if the test results indicate that a trouble does exist, the employee's entry will indicate that further testing by MLT is required. Thus, LMOS allows the existence and status of a pending trouble report to be readily determined.
The third basic service provided by LMOS involves the generating of management and analysis reports by utilizing the information stored in its data base. These reports include analyses of the ARSBs' efficiency and the prediction and identification of problem areas in repair operations.
Finally, because LMOS keeps track of repair force locations and commitments, the system allows for efficient repair force deployment. This is particularly important when a subscriber is requested to remain at a site for repair operations. LMOS, as a provider of these services, clearly represents a material advance over prior manual record and report processing procedures.
An MLT system essentially performs computer controlled tests on the communication lines and interprets the results of those tests. The MLT system obtains information about the normal electrical characteristics of a subscriber's line from the LMOS database and uses it to generate a series of adaptive tests in order to determine the current status of the line. For example, the subscriber may use what is referred to as "inward-only" service, in which outgoing calls on the line are not permitted, and thus no dial tone is provided. There would be little point in running a test to detect a dial tone on such a line. In addition to information about the subscriber's termination equipment, LMOS also contains data describing central office equipment and outside-plant equipment on the line. This data is also required for meaningful MLT testing.
MLT accesses selected lines at and through communication test head hardware. The Test Head first ensures that the voltage on the line to be tested is not high enough to damage the testing equipment. Then, depending upon the manner in which a line is accessed, other preliminary tests may be performed to ascertain whether a given line is available for testing, including for example, whether the line is on intercept, or whether it is currently in use. If the line is available, MLT performs a series of diagnostic tests designed to determine the line's operational status. These tests typically include measurements of AC and DC voltage and current, resistance and capacitance measurements, dial tone detection, dial pulse and DTMF tests and noise checks. In addition, the MLT system can detect the existence of an open wire and determine the location of the break.
The MLT system then interprets the results of these tests in accordance with information acquired from the LMOS data base. Frequently, these results can be used to respond to a subscriber trouble report or inquiry while he is still on the line. In addition, a detailed analysis of the test results can be routed to repair service personnel to enable repair operations to be accomplished quickly and efficiently.
Because of cost and efficiency considerations, however, present implementations of the MLT systems are best suited for use only where the number of lines to be served exceeds 10,000. Each MLT currently relies extensively on the processing power of a single minicomputer, and failure of that machine results in a total failure of the MLT system.